Several species of Campylobacter are known to be associated with wide range of human and animal illnesses, mainly gastroenteritis, colitis, sepsis and urinary tract infections. Recently many studies confirmed the correlation between the presence of C. pyloridis (C. pylori) on the gastric mucosa and duodenal ulceration. The mechanism by which this organism induces ulcer is not clear yet but it is known that colonization of C. pyloridis induces local and systemic immune responses. This antibody response directly correlates with histological diagnosis of chronic or active ulcers as well as renal transplant patients. Therefore, detection of specific antibodies (IgA, IgG, IgM) against this bacteria is a good indication of diagnosis of gastric ulcer. During Phase I of this study four different antigens from C. pyloridis, C. jejuni and C. coli will be prepared. These antigens will be used for development of ELISA and measurement of antibodies in the patient's sera with confirmed medical history of ulcer. Cross reactivity and specificity of these antibodies will be examined with antigens of three different species of Campylobacter (C. fetus, C. jejuni, C. coli) known as a major cause of gastroenteritis but not of gastric ulcer. All antigens will be analyzed by electrophoresis and specific bonds will be identified by Western blotting using positive C. pyloridis sera. During Phase II of this study, species-specific antigen(s) will be purified and characterized. Monoclonal antibodies will be produced for histological examinations as well as for affinity purification of these specific antigens and their use in the development of specific ELISA kits. Finally, after Phase I feasibility studies and Phase II of specific ELISA kit production, we hope that our ELISA test will replace the difficult and expensive procedures such as upper gastrointestinal endoscopy and biopsy, which presently required to demonstrate the presence of C. pyloridis in the stomach.